Getting a new Roku stick due to age of current one

If you mean simply in the sense of failing, most electronic products follow the “bathtub curve” of failure rate.  Ie: lots of failures early, then settling into a low (but non-zero!) failure rate for some time, followed by a rising failure rate later. 

Then there are the questions of: Is it the latest and greatest? Does it do what you need it to do? Do current apps support it etc.  For example, my first personal computer from 1975 still (amazingly) runs, but it fails all the tests in this paragraph.  I keep it for sentimental reasons and because it is cool-looking, but I am not typing this response on it! 😀